Electromagnetic locks are well known and may comprise in one form a solenoid actuated bolt. However, at the present time, it is more common to have an electromagnet mounted to one of a doorway defining means and an attractable armature which is mounted to a door. This arrangement, in one form, may comprise an electromagnet which is recessed or mortised into the soffet of a door and an attractable armature which is carried mortised into or otherwise carried interiorly of the top edge of the door. Such an arrangement is exemplified in copending patent application Ser. No. 014,831 filed Feb. 13, 1987, now U.S. Pat. No. 4,840,411, issued June 20, 1989, and assigned to the assignee of this application. Such electromagnetic locks may also be mounted externally on the door frame on a corresponding vertical surface of the door, as exemplified in U.S. Pat. No. 4,439,808. These types of electromagnetic locks are exemplified in U.S. Pat. No. 4,487,439, and are referred to as electromagnetic shear locks. The holding force of the electromagnetic shear locks magnetically is not as great as the flush electromagnetic locks where the electromagnet engages the armature in a plane essentially parallel to the door to be guarded.
The shear type lock requires mechanical reinforcement, inasmuch as the holding force is not as great as the flush type electromagnetic lock. Flush mounted electromagnetic door lock in which the surfaces of the electromagnet and door mounted armature are parallel to the vertical plane of the door is exemplified in U.S. Pat. Nos. 4,682,801 and 4,573,720. In all of the present installations of electromagnetic locks, the electromagnet is constantly energized to secure the door. This consumes, over a period of time, a substantial amount of electrical energy.
Accordingly, the present invention provides an electromagnetic locking arrangement utilizing an electromagnet of either the shear type or the flush type which is normally deenergized, saving on consumption of electrical power, but will be energized immediately upon a person attempting to gain unauthorized entry into a secured area, while permitting egress of authorized persons within the secured area.